There is a growing recognition of the need for implement steering of towed agricultural implements such as, but not limited to, planters. The need for steering is driven by several factors. First, with increased emphasis on the precision placement of seeds, it is important that the implement be located precisely. Modern auto-steering systems on tractors are capable of keeping the tractor precisely on what is called the A-B line. However, when operating on a hillside or on a contour, the implement will not track on the A-B line but will track inside on the contour and downhill somewhat on the hill side. One solution to keep the implement on the A-B line is to place a GPS receiver on the implement and then guide to tractor off the A-B line such that the implement is on the A-B line. Another solution is to provide the implement with steering capabilities and with a GPS receiver on both the implement and the tractor, guide both the implement and the tractor to stay on the A-B line.
A second need to implement steering is to facilitate alignment of the implement with the desired A-B line after making an end row turn in the field. By steering the implement on the turn rather than relying on the tractor to pull the implement of the desired position, precise placement of the implement is facilitated. A third need for implement steering is to facilitate turning during transport of the implement to and from a field.
Several steering systems for implements have been developed. One system is to use coulters to steer the implement when it is in use in the field. Such a system is available from Orthman Manufacturing under the trade name “Orthman Tracker.” A disadvantage of coulters for steering is that they are only available for steering the implement when the implement is in use in the field. When making end row turns or transporting the implement, the coulters are raised out of the ground. A second steering solution is to equip the ground engaging support wheels of the implement with steering capability. This solves the need for steering on end row turns and transport. However, when the implement is in use in the field, the tires have reduced steering capacity. During use, the planter row units are engaging the ground. Supplemental downforce is applied to the row units by transferring weight from the frame to the row units. This reduces the weight on the tires, reducing the ability of the tires to steer the implement. Thus a need exists for a steering system that is effective both during use in the field as well as during end row turns.